The invention relates to a method for producing an RFID transponder product and RFID transponder products produced according to said method. Here, an RFID transponder product shall be understood as a circuit arrangement having at least one transponder antenna and at least one integrated circuit (also called “chip” in the following) connected to the transponder antenna (in the following also called “antenna structure”), which is embodied for a wireless data transmission to appropriate readers. Typical examples for such planar RFID transponder products are wireless chip cards, identification documents, tickets etc., but also pre-laminates, which at a later time are further processed into the above-mentioned end products.
RFID transponder products can be subject to strong mechanical stress, which leads to particularly high requirements for the integration of the chip into the product as well as the electric connection to the transponder antenna. This stress may arise both during the production process, for example during laminating several layers to each other, as well as during the use of the products.
For this reason, preferably chips in an encapsulated structure are used, in which the chip is arranged in a separate housing. This results in a structural thickness of such ID documents or their preliminary products essentially determined by the thickness of the housed chip. For example, here, particularly the chip modules are used in some types of chip cards, in which the contacting of the chip occurs indirectly via another auxiliary carrier, e.g., a so-called lead frame. Here, the chip is first fastened via the die-bond technology on the lead frame and subsequently the connecting areas of the chip are connected via the wire-bond technology to the lead frame. Then the lead frame is cast with the chip using epoxy resin. The contacting of the chip in a circuit arrangement occurs by contacting the free connectors of the lead frame.
The chips in an encapsulated structure are preferably connected to the ends of a wire antenna comprising several windings and thus the actual RFID element is formed. Such an arrangement is embodied exemplarily in WO 2008/058616 A1.
The processing of naked chips, i.e. chips not arranged in a separate housing, allows a considerable reduction of the structural height of the products, on the one hand, however on the other hand it, increases the risk of the chip breaking and/or the contacts of the chip becoming damaged.
If instead of laying wire antennas, for example comprising several windings of insulated copper wire, planar embodied antenna structures are used, a construction becomes necessary in which one or more antenna windings can be bridged. Using this bridge construction one end of the antenna structure is connected to the first connector of the RFID chip. A second connector of the RFID chip is directly connected to the other end of the antenna structure.
Different constructive variants are known in prior art to realize the necessary electrically conducting bridges, which technologically always require the use of additional contacting material.
For example, in DE 10 2007 054 692 A1 a structure is described for an RFID inlay, in which several antenna sections are arranged on opposite substrate sides of a carrier. At least one penetrating opening is located in the substrate, by which during the metallization an electrically conducting connection is created between the antenna sections arranged on opposite sides of the substrate.
In EP 1 433 368 A1, a structure is shown, in which a tongue of the interior conductor is laid through two cuts over the other substrate side, so that the windings to be crossed are insulated in reference to the tongue by the substrate material.
WO 01/39114 A1 describes a structure, in which an insulating lacquer material is applied between the contacts of the bridge by way of serigraphy. The application of the bridge also occurs by serigraphy of a conducting lacquer coat. Subsequently the application of a protective layer comprising an insulating material occurs, also by way of serigraphy.
WO 98/011507 A1 describes a structure, in which an antenna is created by printing a conducting ink, an insulation by way of printing a dielectric, and a bridge also by printing a conducting ink.
Another example of the embodiment of the bridge construction is disclosed in EP 1 742 173 A2. In a multi-layer card structure, the structure of the antenna coils is located on a carrier layer, comprising a recess, which accepts the lower part of the chip module, i.e. the housed chip. A compensation layer is applied above the carrier layer, which comprises a recess serving to accept the upper part of the chip module, i.e. the lead frame. Additional recesses are provided to embody the antenna bridge.
First, the antenna structure is applied upon the carrier layer, then the compensation layer is laminated thereupon, the chip module with the housed chip is placed onto the antenna structure, and the bridge is printed upon the compensation layer, with all steps being embodied in the sheet format. The electrically conductive bridge is applied directly on the top of the compensation layer, e.g., by printing a conductive paste. The paste is printed here on the top of the compensation layer and here also over the openings.
There is a need for improved RFID transponder products as well as improved methods for the production of such RFID transponder products, in which the tensions acting upon the chip and its contacts can be reduced. The objective of the invention is to develop a constructive arrangement, which on the one hand protects the naked chip inside the layer structure from mechanical stress, allows a technically simple construction to realize the bridge structure, and on the other hand allows a very effective production process using roll-to-roll technologies.
These objectives are attained in a method having the features of claim 1 as well as an RFID transponder product having the features of claim 8. Advantageous embodiments and further developments are described in the dependent claims.
These objectives are attained in a method as well as an RFID transponder product having the features of the present invention.